1. Field of the Invention
The present invention relates to a gas turbine control apparatus and gas turbine output computing method for a single-shaft type combined cycle power plant that comprises a gas turbine, steam turbine and generator, respective rotational shafts of which are connected together to form a single shaft, and a condenser for condensing exhaust steam of the steam turbine.
2. Description of the Prior Art
As a gas turbine control apparatus used for the mentioned single-shaft type combined cycle power plant, such one as disclosed in the Japanese laid-open patent application No. Hei 8-270407, for example, is known. The gas turbine control apparatus disclosed there comprises a vacuum correction factor computing portion for computing a vacuum correction factor based on a condenser vacuum; a steam turbine output computing portion for computing a steam turbine output corrected by multiplying a reference steam turbine output that is computed based on a steam turbine inlet steam pressure by the vacuum correction factor that is computed at the vacuum correction factor computing portion; and a gas turbine output computing portion for computing a gas turbine output by subtracting the steam turbine output that is. computed at the steam turbine output computing portion from a generator output. Control of the output of the gas turbine is done based on the gas turbine output computed at the gas turbine output computing portion.
The present invention is made with an object to provide a gas turbine control apparatus and gas turbine output computing method for a single-shaft type combined cycle power plant by which a gas turbine output can be accurately computed, while a condenser is being washed by what is called a circulating water reversing wash operation where the flow of circulating water or cooling water is switched over for a back wash and ordinary wash of the condenser.
In the course of researches and developments done by the inventors here, such fact as mentioned below has been found.
That is, while the condenser is being washed by the circulating water reversing wash operation, heat exchange action in the condenser is reduced and so the condenser vacuum is also reduced. In the conventional art as mentioned above, no consideration has been paid for the reduction in the condenser vacuum at the time of the circulating water reversing wash operation and so, in the circulating water reversing wash operation time, such a phenomenon occurs that, while the generator output is largely reduced, the steam turbine output is little reduced. Thus, it was found that the gas turbine output, that is computed by subtracting the steam turbine output from the generator output, is miscomputed as if the gas turbine output were reduced. It was also found that an output control of the gas turbine, such as a fuel control, is done based on the miscomputed gas turbine output and there is a possibility that an operation error may arise in the various components and equipments in the power plant.
Based on the result of the mentioned researches and developments, the present invention provides a gas turbine control apparatus for a single-shaft type combined cycle power plant, the single-shaft type combined cycle power plant comprising a gas turbine, steam turbine and generator, respective rotational shafts of which are connected together to form a single shaft, and a condenser for condensing exhaust steam of the steam turbine, the gas turbine control apparatus comprising a vacuum correction factor computing portion for computing a vacuum correction factor based on a condenser vacuum; a steam turbine output computing portion for computing a steam turbine output by multiplying a reference steam turbine output computed based on a steam turbine inlet steam pressure by the vacuum correction factor computed at the vacuum correction factor computing portion; and a gas turbine output computing portion for computing a gas turbine output by subtracting the steam turbine output computed at the steam turbine output computing portion from a generator output, the gas turbine control apparatus being for controlling an output of the gas turbine based on the gas turbine output computed at the gas turbine output computing portion, characterized in that the vacuum correction. factor computing portion comprises a condenser vacuum correcting portion for computing a vacuum down amount in the condenser vacuum caused by a circulating water reversing wash operation while the condenser is in the circulating water reversing wash operation and for correcting the condenser vacuum based on the vacuum down amount and the vacuum correction factor is computed based on the condenser vacuum so corrected at the condenser vacuum correcting portion.
In the gas turbine control apparatus for the single-shaft type combined cycle power plant of the present invention, the vacuum correction factor computing portion comprises the condenser vacuum correcting portion for computing the vacuum down amount in the condenser vacuum caused by the circulating water reversing wash operation while the condenser is in the circulating water reversing wash operation and for correcting the condenser vacuum based on the vacuum down amount and the vacuum correction factor is computed based on the condenser vacuum so corrected at the condenser vacuum correcting portion. Thereby, the vacuum down of the condenser vacuum is reflected in the computation of the gas turbine output at the gas turbine output computing portion. Hence, the gas turbine output can be accurately computed even at the time of the circulating water reversing wash operation. Also, the output control of the gas turbine (fuel control) is done based on the gas turbine output in which the vacuum down of the condenser vacuum is reflected and the operation error of various components and equipments due to the miscomputation of the gas turbine output, as mentioned above, can be prevented.
It is preferable that the condenser vacuum correcting portion comprises a vacuum down amount computing portion for computing the vacuum down amount based on the generator output immediately before the circulating water reversing wash operation. By the condenser vacuum correcting portion so comprising the vacuum down amount computing portion and the vacuum down amount being so computed based on the generator output immediately before the circulating water reversing wash operation, the vacuum down amount can be appropriately computed.
It is preferable that the condenser vacuum correcting portion further comprises a valve opening correction factor computing portion for computing a valve opening correction factor based on a condenser reversing valve opening and the vacuum down amount is corrected based on the valve opening correction factor computed at the valve opening correction factor computing portion. By the condenser vacuum correcting portion so further comprising the valve opening correction factor computing portion and the vacuum down amount being so corrected by the valve opening correction factor computed based on the condenser reversing valve opening, the condenser vacuum that is affected by the opening of the condenser reversing valve can be computed more appropriately.
It is preferable that the condenser vacuum correcting portion further comprises a circulating water temperature correction factor computing portion for computing a circulating water temperature correction factor based on a temperature of circulating water supplied into the condenser and the vacuum down amount is corrected based on the circulating water temperature correction. factor computed at the circulating water temperature correction factor computing portion. By the condenser vacuum correcting portion so further comprising the circulating water temperature correction factor computing portion and the vacuum down amount being so corrected by the circulating water temperature correction factor computed based on the temperature of the circulating water supplied into the condenser, the condenser vacuum that is affected by the temperature of the circulating water as cooling medium of the condenser can be computed further appropriately.
It is preferable that an angle of a compressor inlet guide vane is controlled based on the gas turbine output computed at the gas turbine output computing portion. In this case, an optimal control of the angle of the compressor inlet guide vane becomes possible and a partial load efficiency of the single-shaft type combined cycle power plant can be enhanced.
It is preferable that an opening of a combustor by-pass valve is controlled based on the gas turbine output computed at the gas turbine output computing portion. In this case, control of the opening of the combustor by-pass valve becomes stable to suppress an occurrence of a misfire and reliability of the gas turbine can be enhanced.
Also, the present invention provides a gas turbine output computing method for a single-shaft type combined cycle power plant, the single-shaft type combined cycle power plant comprising a gas turbine, steam turbine and generator, respective rotational shafts of which are connected together to form a single shaft, and a condenser for condensing exhaust steam of the steam turbine, the gas turbine output computing method comprising steps of computing a vacuum correction factor based on a condenser vacuum; computing a steam turbine output by multiplying a reference steam turbine output computed based on a steam turbine inlet steam pressure by the vacuum correction factor; and computing a gas turbine output by subtracting the steam turbine output from a generator output, characterized in further comprising steps of computing a vacuum down amount in the condenser vacuum caused by a circulating water reversing wash operation while the condenser is in the circulating water reversing wash operation; and correcting the condenser vacuum based on the vacuum down amount and computing the vacuum correction factor based on the condenser vacuum so corrected.
In the gas turbine output computing method for the single-shaft type combined cycle power plant of the present invention, the vacuum down amount in the condenser vacuum caused by the circulating water reversing wash operation while the condenser is in the circulating water reversing wash operation is computed; and the condenser vacuum is corrected based on the vacuum down amount and the vacuum correction factor is computed based on the condenser vacuum so corrected. Thereby, the vacuum down of the condenser vacuum is reflected in the gas turbine output that is computed by subtracting the steam turbine output from the generator output. Hence, the gas turbine output can be accurately computed even at the time of the circulating water reversing wash operation.
It is preferable that the vacuum down amount is computed based on the generator output immediately before the circulating water reversing wash operation. By the vacuum down amount being so computed based on the generator output immediately before the circulating water reversing wash operation, the vacuum down amount can be appropriately computed.
It is preferable that a valve opening correction factor is computed based on a condenser reversing valve opening; and the vacuum down amount is corrected based on the valve opening correction factor. By the vacuum down amount being so corrected by the valve opening correction factor computed based on the condenser reversing valve opening, the condenser vacuum that is affected by the opening of the condenser reversing valve can be computed more appropriately.
It is also preferable that a circulating water temperature correction factor is computed based on a temperature of circulating water supplied into the condenser; and the vacuum down amount is corrected based on the circulating water temperature correction factor. By the vacuum down amount being so corrected by the circulating water temperature correction factor computed based on the temperature of the circulating water supplied into the condenser, the condenser vacuum that is affected by the temperature of the circulating water as cooling medium of the condenser can be computed further appropriately.